1. Field of the Invention
This invention relates to a mimeographic printing apparatus of the type in which a stencil can be automatically removed from a printing drum.
2. Description of the Related Art
Heretofore, a rotary mimeographic printing apparatuses having a rotary printing drum is known in which one end of a stencil is secured to the printing drum and is then wound therearound. This prior art is exemplified by Japanese Patent Laid-Open Publication No. 96984/1984. The apparatus of the Japanese Publication No. 96984/1984 includes a clamping piece pivotally supported on an outer surface of the printing drum and a magnetic plate supported on the outer surface of the printing drum for attracting the clamping piece to the outer surface to grip one end of the stencil.
This prior apparatus is suitable to mount a thin stencil like a stencil on the printing drum satisfactorily. After completion of printing process, however, the gripped end of the stencil would sometimes remain adhered to the surface of the magnetic plate owning to the static electricity even after the clamping piece is released from the magnetic plate.
To solve this problem, a printing apparatus equipped with a means for peeling the stencil from the printing drum as the clamping piece is released, has been proposed by Japanese Patent Laid-Open Publication No. 104854/1986.
The prior apparatus of the Japanese Publication No. 104854/1986 includes a pivotable clamping piece selectively attractable to the magnetic plate disposed on the circumference of the printing drum, and an elastic thin piece having one end fixed to the clamping piece and the other end extending over the magnetic plate and fixed to the circumference of the printing drum. When the clamping piece is released from the magnetic plate, the elastic thin piece floats over the magnetic plate, thereby peeling the stencil from the printing drum. With this arrangement, subsequent stencil-removing can be smoothly performed since the stencil already assumes a peeled posture as the clamping piece is released.
Generally, in the foregoing apparatuses, a stencil in the form of a roll is used. In this type of stencil, its end portion apts to be externally curled due to the initial curl in the rolling direction or to the change of conditions during the manufacturing process. If the curling degree is excessive, the following inconvenience would arise; when the clamping piece is released and the stencil is peeled from the magnetic plate, the distal end of the stencil becomes externally curled again. If the curling degree is small, there would be no particular problem in performing the subsequent removing of the stencil. However, if the curling degree is promoted by the factors as temperature, humidity, etc., the removing means could not certainly capture the end of the stencil so that the stencil cannot be removed reliably.